This invention relates to a hydraulic circuit for supplying hydraulic fluid to a plurality of hydraulic drive members found in heavy equipment, such as excavators, backhoes and the like.
In recent years, the use of hydraulic drive systems for controlling the various functions in heavy equipment, such as excavators, has become more common. For example, quite recently, completely hydraulic systems have been developed for use with heavy duty vehicles such as excavators. In such systems, the actuation of control valves that control the flow of fluid to the various drive members is accomplished by hydraulic fluid. One example of such a system incorporates a main hydraulic circuit that includes a pump and a plurality of hydraulically actuated valves that control the flow of fluid between the pump, reservoir and hydraulic motors associated therewith. The valves are self-centering and are opened by a control circuit that is capable of supplying small amounts of fluid under pressure from a source to opposite ends of the valves for actuating the valves. The fluid flow in the control circuit is controlled by a manually operated valve and acts as a "pilot system" for actuating the main control valves.
Such a system has a number of advantages, the primary one being that the function that is being performed can be accurately controlled. For example, utilizing the "pilot system" for actuating the main valves gives the operator the ability to introduce very small amounts of fluid to the hydraulic motors.
While such systems have found a relative degree of success, limitations do exist and areas for improvement have been identified. For example, vehicles incorporating such systems are typically provided with hydraulically operated brakes typically of the hydraulic release type, associated with various of the hydraulic motors. This type of brake is released in response to the application of hydraulic pressure thereto.
One area of improvement that has been identified is the problem of operators trying to operate a hydraulic motor when the brake associated therewith is engaged. This creates problems of brake wear and premature failure and possibly other premature failures in the hydraulic system.